1. Field of the Invention
The present invention relates to hydraulic presses that have very large working surfaces for pressing and forming sheets which are resting on a forming tool. More specifically, the present invention relates to the mechanism used for applying the compressive force to an elastic forming pad which then acts to press the sheets against the forming tool.
2. Description of the Prior Art
In hitherto known presses, very large working surfaces have been utilized to form or mold sheets of various materials on a suitable forming tool. This forming has been achieved by pressing the sheets against the forming tools by means of a forming pad of elastic material. The compressive force is achieved by use of a pressure medium which is pumped into a pressure cell with a bag-like diaphragm located above the forming pad. The diaphragm is formed with an annular bead around an opening and is secured between two disc-shaped attachment members which form an annular slot fitting the bead. The pressure medium space in the pressure cell is then defined by the inner surface of the diaphragm and the lower surface of the attachment member which is located inside the bag-like diaphragm.
Normally the diaphragm and one of the disc-like attachment members have made up one single unit, which is due to the fact that the diaphragm is made of such stiff material that a finished diaphragm cannot be fittd onto the attachment member, and the fact that the bead of the diaphragm has been attached to the attachment member by gluing or vulcanization. Also, in currently known presses, it has been considered absolutely necessary to prevent pressure medium from penetrating in between the attachment members and effect harmful forces, for example, forces tending to remove the attachment members from each other and create unallowable tensile forces in the bolts which hold the attachment members together.
The fact that a diaphragm and a disc-formed attachment member constitute an inseparable unit has several drawbacks. In large presses, for example, with a working surface of 1.5 .times. 5 meters, the disc-formed attachment member has a great weight and involves considerable cost. A spare diaphragm is therefore expensive. Further, the high weight of a spare diaphragm means high transport costs for transporting a diaphragm from a manufacturer and for returning an attachment disc to a diaphragm manufacturer. Particularly in case of damage, when it is desirable to obtain a spare diaphragm rapidly and aircraft transport is desirable, the high weight is a considerable drawback.
The purpose of the present invention is to reduce the above-mentioned drawbacks so that the costs of diaphragms are reduced and transport and handling of diaphragms are facilitated.